The present invention relates to crosslinkable, especially photocross-linkable, bi-reactive liquid crystalline compounds, to liquid crystalline mixtures comprising such compounds and to the use thereof in the crosslinked state as optical components.
Photocrosslinkable liquid crystals provided with a suitable amount of a photoinitiator can be oriented on a substrate or in a cell by means of suitable orientation layers or in a force field, and can then be crosslinked in that state by irradiation with light of-a suitable wavelength. The resulting structure is retained even at high temperatures. Thus, optical components, such as, for example, waveguides, optical gratings, filters and retarders, piezoelectric cells and cells having non-linear optical (NLO) properties, etc., can be produced. Such optical components can be used, for example, for frequency doubling (SHG) or in colour filters.
Further properties, such as, for example, the birefringence, the refractive index, the transparency, etc., must satisfy different requirements depending on the field of application. For example, materials for optical filters should have high birefringence xcex94n combined with low dispersion n=f(xcex).
In addition to the general utility of polymerisable i.e. crosslinkable liquid crystals for optical components, such liquid crystalline materials are suitable for cladding glass fibres for optical data transmission. The use of such materials increases the elastic modulus in the longitudinal axis of the fibre, lowers the thermal expansion coefficients and reduces microdistortion losses. This results in increased mechanical stability. Moreover, cross-linkable liquid crystals have an anisotropic thermal conductivity that enables heat to flow in specific directions.
The crosslinkable liquid crystals must have good chemical and thermal stability, good solubility in usual solvents and good stability towards electric fields and electromagnetic radiation. They should have a suitable mesophase in a temperature range from about 25xc2x0 C. to about +100xc2x0 C., especially from about 25xc2x0 C. to about +80xc2x0 C. It is also important that the components have good miscibility with one another since liquid crystals are generally used in the form of mixtures of several components.
For use in optical retarders, polarisation interference filters (for example Solc filters) etc., it is necessary, in addition, for the optical anisotropy to be as great as possible (xcex94n=|nexe2x88x92no|) while the absorption wavelength is as short as possible., In that manner, the desired optical retardation can be obtained with sufficiently thin LCP films (LCP stands for liquid crystalline polymer).The same applies also to use in cholesteric filters, since the band width of the selective reflection is proportional to the optical anisotropy xcex94n.
Conventional photochemically oligomerisable or polymerisable liquid crystals generally have a high melting point and a high clearing point and medium optical anisotropy. Firstly, the high melting point has the disadvantage that during processing spontaneous thermal polymerisation may occur prematurely at just above the melting point. This spontaneous polymerisation leads to the formation of domains, resulting in significant impairment of the optical and thermal properties of the crosslinked layers produced. Secondly, a small temperature difference between the melting point and the clearing point results in a low degree of ordering and thus in a low degree of optical anisotropy. The melting point can be lowered by producing complex mixtures having several components, which enables processing to be carried out at lower temperatures but entails the risk of crystallisation of conventional polymerisable liquid crystals. Photochemically oligomerisable or polymerisable compounds are described, for example, in EP-A-0 331 233.
It is accordingly an object of the present invention to provide oligomerisable or polymerisable i.e. crosslinkable compounds that, on their own or in mixtures, have an optical anisotropy that is as great as possible while the absorption wavelength is as short as possible, especially for use in optical components. They should also have low melting points and high clearing points so that during processing as high a degree of ordering as possible and thus a high degree of optical anisotropy of the LCP film is obtained at just above the melting point. It should further be possible to orient and structure the compounds without domains, and they should also have excellent thermal stability and long-term stability in the crosslinked state. Conventional photochemically oligomerisable or polymerisable liquid crystals generally have only medium optical anisotropy.
The present invention now provides compounds that are outstandingly suitable as individual components or as components of liquid crystal mixtures for the above-mentioned applications.
The present invention relates to compounds of the general formula I: 
wherein
R1, R2 each independently of the other represents a crosslinkable group, such as CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94Phxe2x80x94, CH2xe2x95x90CHxe2x80x94COxe2x80x94NHxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(Ph)xe2x80x94CONHxe2x80x94, CH2xe2x95x90C(COORxe2x80x2)xe2x80x94CH2xe2x80x94COOxe2x80x94, (Rxe2x80x2OOC)xe2x80x94CH2xe2x80x94Cxe2x95x90CH2xe2x80x94COOxe2x80x94, CH2xe2x95x90CHxe2x80x94Oxe2x80x94, CH2xe2x95x90CHxe2x80x94OOCxe2x80x94, CHxe2x95x90CHxe2x80x94Phxe2x80x94, cis- or trans-xe2x80x94HOOxe2x80x94CRxe2x80x2xe2x95x90CRxe2x80x2xe2x80x94COOxe2x80x94, siloxane, 
wherein (Ph) represents phenyl, Ph represents phenylene, Rxe2x80x2 represents lower alkyl and Rxe2x80x3 represents methyl, methoxy, cyano or halogen;
S1, S2 each independently of the other represents a spacer unit, such as a straight-chain or branched alkylene grouping xe2x80x94(CH2)rxe2x80x94 which may optionally be mono- or poly-substituted by fluorine, or xe2x80x94((CH2)2xe2x80x94O)rxe2x80x94, or a chain of the formula xe2x80x94(CH2)rxe2x80x94Yxe2x80x94(CH2)sxe2x80x94 which may optionally be mono- or poly-substituted by fluorine, wherein Y is a single bond or a linking functional group, such as xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94NR3xe2x80x94, xe2x80x94NR3xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94NR3xe2x80x94, xe2x80x94NR3xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94NR3xe2x80x94, xe2x80x94NR3xe2x80x94COxe2x80x94NR3xe2x80x94, xe2x80x94Oxe2x80x94OCxe2x80x94Oxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94, wherein R3 represents hydrogen or lower alkyl and r and s are each an integer from 0 to 20, with the proviso that 2xe2x89xa6r+sxe2x89xa620, or xe2x80x94(Si[(CH3)2]O)uxe2x80x94, xe2x80x94O(CH2)t(Si[(CH3)2]O)uSi[(CH3)2](CH2)tOxe2x80x94, or xe2x80x94NH(CH2)t(Si[CH3)2]O)uSi[(CH3)2](CH2)tNHxe2x80x94, wherein t is an integer from 1 to 12 and u is an integer from 1 to 16, with the proviso that 2t+uxe2x89xa620;
with the proviso that R1xe2x80x94S1 and R2xe2x80x94S2 do not contain any xe2x80x94Oxe2x80x94Oxe2x80x94 or xe2x80x94Nxe2x80x94Oxe2x80x94 groups;
A, C and D represent 
B represents 
wherein also at least one of the phenylene rings in A, B, C or D may be replaced by a 1,4-phenylene ring in which one or two non-adjacent CH groups have been replaced by nitrogen; and
L1, L2, L3 each independently of the others represent hydrogen, C1-C20-allyl, C2-C20-alkenyl, C1-C20-alkoxy, C2-C20-alkenylpxy, C1-C20-alkoxycarbonyl, formyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy or nitro,
with the proviso that in at least one phenylene ring in A, B, C or D one of the mentioned substituents is other than hydrogen;
k, l, m are O or 1, wherein k+I+m must be equal to 1 or 2; and
Z1, Z2, Z3 each independently of the others represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94(CH2)3Oxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94.
In the structural formulae of the present Application, broken lines ( - - - orxe2x80x94) are used to denote linkages with the adjacent element by a single bond.
Where necessary, the above-used terms will be explained hereinafter.
xe2x80x9cHalogenxe2x80x9d embraces, in the context of the present invention, fluorine, chlorine, bromine, iodine, especially fluorine and chlorine.
xe2x80x9cLower alkylxe2x80x9d represents, in the context of the present invention, a straight-chain or branched alkyl group having from 1 to 4 carbon atoms, such as, for example, methyl, ethyl, propyl, butyl, isopropyl, isobutyl, tert-butyl, but especially methyl, ethyl, propyl or butyl.
The terms C1-C20-alkyl, C1-C20-alkoxy, C1-C20-alkoxycarbonyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy embrace, in the context of the present invention, straight-chain or branched saturated hydrocarbon radicals having up to 20 carbon atoms, such as, for example, methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, methyloxy, ethyloxy, n-propiloxy, isopropyloxy, butyloxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl, octyloxycarbonyl, nonyloxycarbonyl, decyloxycarbonyl, undecyloxycarbonyl, dodecyloxycarbonyl, methylcarbonyl, ethylcarbonyl, propylcarbonyl, butylcarbonyl, pentylcarbonyl, hexylcarbonyl, octylcarbonyl, nonylcarbonyl, decylcarbonyl, undecylcarbonyl, dodecylcarbonyl, methylcarbonyloxy, ethylcarbonyloxy, propylcarbonyloxy, butylcarbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, octylcarbonyloxy, nonylcarbonyloxy, decylcarbonyloxy, undecylcarbonyloxy, dodecylcarbonyloxy, and the like.
The terms C2-C20-alkenyl and C2-C20-alkenyloxy embraces, in the context of the present invention, alkenyl groups having from 2 to 20 carbon atoms, such as 2-alkenyl, 3-alkenyl, 4-alkenyl and alkenyl having a terminal double bond, such as, for example, allyl, 3-butenyl, 4-pentenyl, 5-hexenyl, 6-heptenyl, 7-octenyl, 8-nonenyl, 9-decenyl, 10-undecenyl, allyloxy, 3-butenyloxy, 4-pentenyloxy, 5-hexenyloxy, 6-heptenyloxy, 7-octenyloxy, 8-nonenyloxy, 9-decenyloxy, 10-undecenyloxy and the like.
When any of L1, L2, L3 represents C2-C20-alkenyloxy, it may either be a polymerisable group wherein the carbon atom bearing a double bond is directly linked to the oxygen atom, i.e. with the double bond in the 1-position; or a C3-C20-alkenyloxy group, wherein the carbon atom bearing a double bond is not directly linked to the oxygen atom.
Such compounds have a surprisingly high degree of optical anisotropy (xcex94n). Moreover, as components in suitable mixtures they bring about good orientability on orientation layers, which is important, for example, for good contrast.
Preferred compounds of formula I are compounds of formulae I-A to I-G 
wherein
Z4, Z5 each independently of the other represents a single bond, xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94; and
R1, R2, S1, S2, L1, L2 and L3 are as defined for formula I.
Special preference is given to the compounds of formulae I-A, I-B, I-D, I-F and I-G.
Of the compounds of formula I-A, special preference is given to the compounds of formulae I-A-1 and I-A-2
wherein
L1, L2, L3 each independently of the others represents hydrogen, C1-C20-alkyl, C2-C20-alkenyl, C1-C20-alkoxy or C2-C20-alkenyloxy, wherein at least one substituent must be other than hydrogen;
Z4 represents xe2x80x94Cxe2x89xa1Cxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, especially xe2x80x94COOxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, more especially xe2x80x94COOxe2x80x94; and
R1, R2, S1, S2 are as defined for formula I.
Of the compounds of formula I-B, special preference is given to the compounds of formula I-B-1
wherein
R1, R2, S1, S2, Z4, L1, L2, L3 are as defined for formula I-A-1.
Of the compounds of formula I-D, special preference is given to the compounds of formulae I-D-1 and I-D-2: 
wherein
R1, R2, Z4, L1, L2, L3 are as defined for formula I-A-1.
Of the compounds of formula I-F, special preference is given to the compounds of formula I-F-1
wherein
Z5 represents a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94COOxe2x80x94, especially a single bond; and
R1, R2, Z4, L1, L2, L3 are as defined for formula I-A-1.
Of the compounds of formula I-G, special preference is given to the compounds of formula I-G-1
wherein
R1, R2, Z4, L1, L2, L3 are as defined for formula I-A-1.
More especially preferred compounds of formulae I-A-1, I-A-2, I-B-1, I-D-1, I-D-2, I-F-1 and I-G-1 are those wherein the group 
is defined by 
wherein L11, L12 each independently of the other represents C1-C20-alkyl, C2-C20-alkenyl, C1-C20-alkoxy or C2-C20-alkenyloxy, especially C1-C12-alkoxy.
The compounds of formula I according to the invention are very easy to obtain synthetically. They can be prepared, for example, analogously to the methods shown in the following Schemes in a manner known per se.
The following abbreviations are used:
DCM dichloromethane
DME dimethoxyethane
DMSO dimethyl sulphoxide
THF tetrahydrofuran
EDC N-(3-dimethylaminopropyl)-Nxe2x80x2-ethylcarbodiimide hydrochloride
DEAD azodicarboxylic acid diethyl ester (diethyl azodicarboxylate)
DMAP 4-(dirnethylamino)pyridine
TPP triphenylphosphine 
The compounds of formulae I can be used as pure compounds or in the form of mixtures with one another and/or with other liquid crystal components.
The liquid crystalline mixtures according to the invention comprise at least 2 components, of which at least one component is a compound of formula I. A second component and any further components may be further compounds of formula I or other, known liquid crystalline compounds which may have one or more crosslinkable groups. The mixture may also comprise one or more chiral components or isotropic doping agents.
By virtue of the good solubility of the compounds of formula I and by virtue of their good miscibility with one another, the proportion of compounds of formula I in the mixtures according to the invention may be high and may be up to 99% by weight.
The mixtures according to the invention preferably comprise, in addition to one or more compounds of formula I, one or more compounds from the group of compounds of the general formulae 
wherein
R4 represents a polymerisable group, such as CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94Oxe2x80x94, CH2xe2x95x90CHxe2x80x94COOxe2x80x94, CH2xe2x95x90C(CH3)xe2x80x94COOxe2x80x94, CH2xe2x95x90C(Cl)xe2x80x94COOxe2x80x94 or 
S3, S4 each independently of the other is xe2x80x94(CH2)nxe2x80x94 or xe2x80x94O(CH2)nxe2x80x94;
E1, E2 each independently of the other represents 1,4-phenylene, trans-1,4-cyclohexylene, pyridine-2,5-diyl, pyrimidine-2,5-diyl or trans-1,4-cyclohexylene-1,4-phenylene;
F1, F2 each independently of the other represents 1,4-phenylene or 2- or 3-fluoro-1,4-phenylene;
L4, L5, L6 each independently of the others represents hydrogen, C1-C20-alkyl, C2-C20-alkenyl, C1-C20-alkoxy, C1-C20-alkoxy-carbonyl, formyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy, halogen, cyano or nitro;
Z6 represents xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94OOC(CH2)2xe2x80x94 or xe2x80x94COO(CH2)3xe2x80x94;
Z7 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)3xe2x80x94, xe2x80x94(CH2)3xe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94;
Z8 represents a single bond, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OOCxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94;
each X independently of any other(s) represents hydrogen, C1-C20-alkyl, C2-C20-alkenyl, C1-C20-alkoxy, C1-C20-alkoxycarbonyl, formyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy, fluorine, chlorine, bromine, cyano or nitro;
n is an integer from 2 to 20; and
v is an integer from 2 to 12.